The present invention relates to a method and apparatus for forming a homogeneous mass of comminuted smokable material, especially for forming a homogeneous mass of tobacco shreds. More particularly, the invention relates to improvements in a method and apparatus for forming a homogeneous mass which consists of tobacco shreds or the like and can be converted into the filler of a continuous rod, such as cigarette rod.
U.S. Pat. No. 3,138,163 discloses a cigarette rod making machine wherein a sifting device separates short and medium long shreds from long shreds and fragments of tobacco ribs. The separated short and medium long shreds are caused to form a first layer, and the separated long shreds and fragments of tobacco ribs are showered onto the first layer to form thereon a second layer, i.e., the two layers jointly contain all of the ingredients of the agglomeration of shreds and fragments of ribs which were delivered to the sifting device. The material of the two layers is then introduced into a suction air stream which entrains the short, medium long and long shreds (i.e., the particles which are obtained in response to comminution of tobacco leaf laminae) but is incapable of entraining the relatively heavy and bulky fragments of tobacco ribs. In this manner, the fragments of ribs are segregated from the shreds and the shreds are used to form a tobacco stream which is ready to be draped into cigarette paper or the like.
A drawback of the patented apparatus is that it cannot ensure reliable segregation of all fragments of ribs which could interfere with the formation of a satisfactory tobacco stream and also that the apparatus cannot effect predictable disintegration of clumps or lumps of tobacco shreds which are normally present in the material that is being fed to the sifting device.